Combination stylet and straightening coating for a cochlear implant electrode array

ABSTRACT

A cochlear implant electrode assembly device ( 10 ) comprising an elongate electrode carrier member ( 11 ), a stiffening element ( 15 ), and a stiffening sheath ( 16 ) that at least partially envelops the elongate member ( 11 ). The member ( 11 ) is made of a resiliently flexible first material and has a plurality of electrodes ( 12 ) mounted thereon. The member ( 11 ) has a first configuration that allows it to be inserted into an implantee&#39;s cochlea ( 30 ). The member ( 11 ) also has a second configuration wherein the member is curved to match an inside surface of the cochlea ( 30 ), and at least one intermediate configuration between the first and second configurations. Both the stiffening element ( 15 ) and sheath ( 16 ) are made of a material that is relatively stiffer than the member ( 11 ). The stiffening element ( 15 ) and the stiffening sheath ( 16 ) in combination bias the elongate member ( 11 ) into the first configuration. If either the stiffening element ( 15 ) or the stiffening sheath ( 16 ) is removed or deactivated, the elongate member ( 11 ) adopts an intermediate configuration.

FIELD OF THE INVENTION

[0001] The present invention relates to an implantable device and, inparticular, to an implantable cochlear electrode assembly.

BACKGROUND OF THE INVENTION

[0002] Hearing loss, which may be due to many different causes, isgenerally of two types, conductive and sensorineural. Of these types,conductive hearing loss occurs where the normal mechanical pathways forsound to reach the hair cells in the cochlea are impeded, for example,by damage to the ossicles. Conductive hearing loss may often be helpedby use of conventional hearing aid systems, which amplify sound so thatacoustic information does reach the cochlea and the hair cells.

[0003] In many people who are profoundly deaf, however, the reason fordeafness is sensorineural hearing loss. This type of hearing loss is dueto the absence of, or destruction of, the hair cells in the cochleawhich transduce acoustic signals into nerve impulses. These people arethus unable to derive suitable benefit from conventional hearing aidsystems, because there is damage to or absence of the mechanism fornerve impulses to be generated from sound in the normal manner.

[0004] It is for this purpose that cochlear implant systems have beendeveloped. Such systems bypass the hair cells in the cochlea anddirectly deliver electrical stimulation to the auditory nerve fibres,thereby allowing the brain to perceive a hearing sensation resemblingthe natural hearing sensation normally delivered to the auditory nerve.U.S. Pat. No. 4,532,930, the contents of which are incorporated hereinby reference, provides a description of one type of traditional cochlearimplant system.

[0005] Cochlear implant systems have typically consisted of two keycomponents, namely an external component commonly referred to as aprocessor unit, and an implanted internal component commonly referred toas a stimulator/receiver unit. Traditionally, both of these componentshave cooperated together to provide the sound sensation to an implantee.

[0006] The external component has traditionally consisted of amicrophone for detecting sounds, such as speech and environmentalsounds, a speech processor that converts the detected sounds andparticularly speech into a coded signal, a power source such as abattery, and an external antenna transmitter coil.

[0007] The coded signal output by the speech processor is transmittedtranscutaneously to the implanted stimulator/receiver unit situatedwithin a recess of the temporal bone of the implantee. Thistranscutaneous transmission occurs through use of an inductive couplingprovided between the external antenna transmitter coil which ispositioned to communicate with an implanted antenna receiver coilprovided with the stimulator/receiver unit. This communication servestwo essential purposes, firstly to transcutaneously transmit the codedsound signal and secondly to provide power to the implantedstimulator/receiver unit. Conventionally, this link has been in the formof a radio frequency (RF) link, but other such links have been proposedand implemented with varying degrees of success.

[0008] The implanted stimulator/receiver unit typically included theantenna receiver coil that receives the coded signal and power from theexternal processor component, and a stimulator that processes the codedsignal and outputs a stimulation signal to an intracochlea electrodeassembly which applies the electrical stimulation directly to theauditory nerve producing a hearing sensation corresponding to theoriginal detected sound.

[0009] The external componentry of the cochlear implant has beentraditionally carried on the body of the implantee, such as in a pocketof the implantee's clothing, a belt pouch or in a harness, while themicrophone has been mounted on a clip mounted behind the ear or on aclothing lapel of the implantee.

[0010] More recently, due in the main to improvements in technology, thephysical dimensions of the speech processor have been able to be reducedallowing for the external componentry to be housed in a small unitcapable of being worn behind the ear of the implantee. This unit hasallowed the microphone, power unit and the speech processor to be housedin a single unit capable of being discretely worn behind the ear, withthe external transmitter coil still positioned on the side of the user'shead to allow for the transmission of the coded sound signal from thespeech processor and power to the implanted stimulator unit.

[0011] Together with improvements in available technology much researchhas been undertaken in the area of understanding the way sound isnaturally processed by the human auditory system. With such an increasedunderstanding of how the cochlea naturally processes sounds of varyingfrequency and magnitude, there is a need to provide an improved cochlearimplant system that delivers electrical stimulation to the auditorynerve in a way that takes into account the natural characteristics ofthe cochlea.

[0012] It is known in the art that the cochlea is tonotopically mapped.In other words, the cochlea can be partitioned into regions, with eachregion being responsive to signals in a particular frequency range. Thisproperty of the cochlea is exploited by providing the electrode assemblywith an array of electrodes, each electrode being arranged andconstructed to deliver a cochlea-stimulating signal within a preselectedfrequency range to the appropriate cochlea region. The electricalcurrents and electric fields from each electrode stimulate the ciliadisposed on the modiola of the cochlea. Several electrodes may be activesimultaneously.

[0013] It has been found that in order for these electrodes to beeffective, the magnitude of the currents flowing from these electrodesand the intensity of the corresponding electric fields, are a functionof the distance between the electrodes and the modiola. If this distanceis relatively great, the threshold current magnitude must be larger thanif the distance is relatively small. Moreover, the current from eachelectrode may flow in all directions, and the electrical fieldscorresponding to adjacent electrodes may overlap, thereby causingcross-electrode interference. In order to reduce the thresholdstimulation amplitude and to eliminate cross-electrode interference, itis advisable to keep the distance between the electrode array and themodiola as small as possible. This is best accomplished by providing theelectrode array in the shape which generally follows the shape of themodiola. Also, this way the delivery of the electrical stimulation tothe auditory nerve is most effective as the electrode contacts are asclose to the auditory nerves that are particularly responsive toselected pitches of sound waves.

[0014] In order to achieve this electrode array position close to theinside wall of the cochlea, the electrode needs to be designed in such away that it assumes this position upon or immediately followinginsertion into the cochlea. This is a challenge as the array needs to beshaped such that it assumes a curved shape to conform with the shape ofthe modiola and must also be shaped such that the insertion processcauses minimal trauma to the sensitive structures of the cochlea. Inthis sense it has been found to be desirable for the electrode array begenerally straight during the insertion procedure.

[0015] Several procedures have been adopted to provide an electrodeassembly that is relatively straightforward to insert while adopting acurved configuration following insertion in the cochlea. In one case, aplatinum wire stylet is used to hold a pre-curved electrode array in agenerally straight configuration up until insertion. Followinginsertion, the platinum stylet is withdrawn allowing the array to returnto its pre-curved configuration. While such an arrangement has provedbeneficial, penetration of the wall of the cochlea is possible if thesurgeon does not insert the array using an appropriate rate andorientation, or withdraw the stylet at the appropriate end point duringinsertion of the assembly.

[0016] In another development, a bimetallic filament (such asnickel/titanium) or a shape memory alloy (eg. an alloy of nickel andtitanium) is positioned in the electrode assembly and used to again holda pre-curved electrode array in a generally straight configuration whilethe array is at about room temperature. On insertion into the body andexposure to body temperature, the alloy or filament bends into apre-selected curved configuration.

[0017] In a still further arrangement, a longitudinal element that isarranged on one side of the array and constructed to change itsdimension on insertion can be utilised. For example, the longitudinalelement could include a hydrogel, such as polyacrylic acid (PAA) orpolyvinyl alcohol (PVA), which expands after insertion by absorbingwater from the cochlear fluid.

[0018] In developing such electrode array designs, it is of greatimportance that the design be constructed to minimise potential damageto sensitive structures in the cochlear on insertion and placement. Forexample, in the case of use of platinum stylets, some studies suggestthat wall penetration is a problem in about 20% of cases. Each of theabove constructions suffer from a number of disadvantages in thisregard.

[0019] The present invention is directed to an electrode assemblyadapted to overcome some of the difficulties of prior art electrodeassemblies.

[0020] Any discussion of documents, acts, materials, devices, articlesor the like which has been included in the present specification issolely for the purpose of providing a context for the present invention.It is not to be taken as an admission that any or all of these mattersform part of the prior art base or were common general knowledge in thefield relevant to the present invention as it existed before thepriority date of each claim of this application.

SUMMARY OF THE INVENTION

[0021] Throughout this specification the word “comprise”, or variationssuch as “comprises” or “comprising”, will be understood to imply theinclusion of a stated element, integer or step, or group of elements,integers or steps, but not the exclusion of any other element, integeror step, or group of elements, integers or steps.

[0022] According to a first aspect, the present invention is animplantable tissue-stimulating device comprising:

[0023] an elongate member having a plurality of electrodes mountedthereon and having a first configuration that allows said member to beinserted into an implantee's body, a second configuration wherein saidelongate member is adapted to apply a preselected tissue stimulationwith the electrodes, and at least one intermediate configuration betweensaid first and second configurations, said elongate member being made ofa resiliently flexible first material;

[0024] a stiffening element made of a material relatively stiffer thansaid first material; and

[0025] a stiffening sheath at least partially enveloping said elongatemember and made of a material relatively stiffer than said firstmaterial;

[0026] wherein said stiffening element and said stiffening sheath incombination bias said elongate member into said first configuration andfurther wherein if either the stiffening element or the stiffeningsheath is removed or deactivated, the elongate member adopts said atleast one intermediate configuration.

[0027] In a preferred embodiment, the second configuration of theelongate member is curved. More preferably, the elongate member adopts aspiral configuration when in the second configuration.

[0028] According to a second aspect, the present invention is a cochlearimplant electrode assembly including:

[0029] an elongate electrode carrier member having a plurality ofelectrodes mounted thereon and having a first configuration that allowssaid member to be inserted into an implantee's cochlea, a secondconfiguration wherein said elongate member is curved to match an insidesurface of said cochlea, and at least one intermediate configurationbetween said first and second configurations, said elongate member beingmade of a resiliently flexible first material;

[0030] a stiffening element made of a material relatively stiffer thansaid first material; and

[0031] a stiffening sheath at least partially enveloping said elongatemember and made of a third material relatively stiffer than said firstmaterial;

[0032] wherein said stiffening element and said stiffening sheath incombination bias said elongate member into said first configuration andfurther wherein if either the stiffening element or the stiffeningsheath is removed or deactivated, the elongate member adopts said atleast one intermediate configuration.

[0033] The elongate member is preferably preformed from a plasticsmaterial with memory and is preformed to the second configuration. Theelongate member preferably has a first end that is firstly inserted intothe implantee.

[0034] In a preferred embodiment, the first configuration is preferablysubstantially straight. More preferably, the first configuration isstraight.

[0035] In a preferred embodiment, the elongate member is formed from asuitable biocompatible material. In one embodiment, the material can bea silicone, such as a flexible silicone elastomer-Silastic. Silastic MDX4-4210 is an example of one suitable silicone for use in the formationof the elongate member. In another embodiment, the elongate member canbe formed from a polyurethane.

[0036] In a further embodiment, the elongate member can have aresiliently flexible tip member extending forwardly from the first endof the body. The tip member preferably has a distal end and a proximalend. The tip member can have a stiffness that is relatively less stiffthan said stiffening element. The tip member can further be formed of amaterial that is substantially the same or the same stiffness as thebody of the elongate member. In another embodiment, the tip member canbe formed of a material that is relatively less stiff than at least aportion of the elongate member. In a further embodiment, the tip membercan be formed of a material that undergoes a change in stiffness,preferably a decrease in stiffness, on insertion into the body, such asthe cochlea.

[0037] In a further embodiment, the stiffness of the tip member can varyalong at least a portion of its length from its distal end to itsproximal end. In one embodiment, the stiffness of the tip member canvary over the entire length of the tip member or only a portion thereof.The stiffness can increase from the distal end to the proximal end. Inone embodiment, the stiffness of the tip member over said portion or itslength can increase gradually from its distal end towards to theproximal end. The increase in stiffness can be substantially smooth orincrease in a stepwise fashion.

[0038] In a further embodiment, the tip member can be formed of the samematerial as the body of the elongate member. In another embodiment, thetip member can be formed of a different material to that of the body ofthe elongate member. The tip member can be comprised of an innerrelatively stiff core of material having a tapered end, with at leastthe tapered end being overlaid by a relatively flexible material thatextends beyond the tapered end of the core material so that the tipmember undergoes a gradual decrease in flexibility in the region of thetapered end of the core moving away from the distal end.

[0039] The tip member can be formed separately to the body of theelongate member and mounted thereto. For example, the tip member can beadhered to the first end of the body of the elongate member. In anotherembodiment, the tip member can be integrally formed with the body of theelongate member. The tip member can be formed from a silicone material.In another embodiment, the tip member can be formed of an elastomericmaterial, such as polyurethane.

[0040] In another embodiment, the tip member can have a plurality ofmetallic particles dispersed therethrough. The metallic particles can besubstantially evenly dispersed through the tip member. Alternatively,the metallic particles can be non-evenly dispersed throughout the tipmember. In one embodiment, the metallic particles can increase indensity away from the distal end towards the proximal end of the tipmember. By varying the density of the metallic particles, it is possibleto vary the relative stiffness of the tip member.

[0041] The metallic particles preferably comprise a biocompatiblematerial, such as platinum. The particles can be substantially sphericalor spherical. It will be appreciated that the particles can have othersuitable shapes. In one embodiment, the particles can have a diameterbetween about 50 μm and 100 μm.

[0042] In addition to, or instead of, being used to potentially modifythe physical characteristics of the tip member, the provision of themetallic particles also result in the tip member being detectable byfluoroscopy and X-ray techniques. This provides another means for thesurgeon to monitor the placement and position of the tip member duringor after insertion of the electrode array in the body, such as in thecochlea.

[0043] When the elongate member is in the first configuration, the tipmember is preferably substantially straight and, more preferably,straight.

[0044] In a further embodiment, the tip member can be coated with alubricious material. The lubricious material can be a bioresorbable ornon-bioresorbable material.

[0045] The tip member can be formed from, or incorporate as a portionthereof, a bioresorbable material. The presence of the bioresorbablematerial preferably results in the flexibility of the tip memberincreasing on insertion of the tip member into the body, such as thecochlea. The bioresorbable material in the tip member can be selectedfrom the group consisting of polyacrylic acid (PAA), polyvinyl alcohol(PVA), polylactic acid (PLA) and polyglycolic acid (PGA).

[0046] In another embodiment, the tip member can be formed from, orincorporate as a portion thereof, a polymeric coating which becomessofter, and so increases in resilient flexibility, in the presence ofmoisture or body heat.

[0047] The tip member preferably has a length from its distal end to itsproximal end in the range of about 0.3 to 4 mm, more preferably about1.0 to 3 mm. The diameter of the tip member can be substantiallyconstant for a majority of its length or can vary in diameter. The tipmember can be substantially cylindrical, cylindrical, or non-cylindricalfor a majority of its length. At the distal end, the diameter preferablygradually decreases to form a rounded end. The maximum diameter of thetip member is preferably about 0.55 mm.

[0048] In one embodiment, the tip member can be solid. In anotherembodiment, the tip member can have an external wall defining a cavity.In one embodiment, the cavity can have a diameter greater than that ofthe receiving portion of the body of the elongate member. In a furtherembodiment, the cavity can extend from the proximal end towards thedistal end of the tip member. The cavity can decrease in diameter awayfrom the proximal end. The cavity can be in communication with a distalend of the receiving portion of the body of the elongate member. In afurther embodiment, the stiffening means can extend into the cavity whenpositioned within the device or assembly according to the respectiveaspects of the present invention. In a preferred embodiment, the tipmember can move relative to the stiffening means when it extends intothe cavity of the tip member.

[0049] In general, the tip could be made of a combination of materialsarranged in a variety of geometries depending on the specific designgoal. The outside shape and size of the tip can also be made in avariety of forms depending on the design goal.

[0050] In one embodiment, the stiffening element is formed of abioresorbable material which softens or dissolves on exposure to afluid. The stiffening element can soften or dissolve on exposure to asaline solution or a body fluid of the implantee, such as cochlearfluid.

[0051] In a further embodiment, the bioresorbable material of thestiffening element is selected from the group consisting of polyacrylicacid (PAA), polyvinyl alcohol (PVA), polylactic acid (PLA) andpolyglycolic acid (PGA). It is envisaged that other similar materialscould also be used.

[0052] In another embodiment, the stiffening element can be formed froma non-bioresorbable material. In this embodiment, the stiffening elementcan comprise a metallic stylet, or a stylet from any other suitablestiffening material, extending through a lumen in the elongate member.In one embodiment, the stylet can be formed from a biocompatiblematerial, such as a metal, metallic alloy or a stiff plastic. In apreferred embodiment, a metal stylet can be formed from platinum.

[0053] In a still further embodiment, the stiffening element can beformed from a shape memory alloy or a heat sensitive material. Forexample, the stiffening element can be formed from a nickel/titaniumalloy, or a bimetallic element formed of a laminate of two differentmetals, that is shaped to take a straight or substantially straightconfiguration at room temperature but bends into another shape once itis exposed to body temperature.

[0054] In one embodiment, the lumen for the stylet can be cylindricaland also can have an opening formed therein. In the case of a metalstylet, the stylet can extend out of the opening allowing the stylet tobe manipulated and removed from the lumen during or following insertionof the device. In the case of a bioresorbable stiffening element, theopening can act as a fluid ingress means allowing body fluids to enterthe lumen on insertion of the device into an implantee.

[0055] Where the stiffening element is a metallic or metallic alloy orplastic stylet, the stiffening sheath is preferably formed of abioresorbable material which dissolves or softens on exposure to afluid. The stiffening sheath can dissolve or soften on exposure to asaline solution or a body fluid of the implantee, such as cochlearfluid.

[0056] In a further embodiment, the bioresorbable material of thestiffening sheath is selected from the group consisting of polyacrylicacid (PAA), polyvinyl alcohol (PVA), polylactic acid (PLA) andpolyglycolic acid (PGA). It is also envisaged that other suitablematerials could also be used.

[0057] The device can include an additional layer surrounding thestiffening sheath. The additional layer can have a first rate of fluidingress therethrough and have at least one fluid ingress means formedtherein, the rate of fluid ingress through the fluid ingress means beinggreater than the first rate of fluid ingress through the additionallayer.

[0058] The fluid ingress means can comprise one or more openings in theadditional layer. The openings can be closable. The openings cancomprise slits in the additional layer. The slits can be formed to allowsubstantially the same or the same rate of ingress of fluid through theadditional layer. In another embodiment, at least one slit can allow adifferent rate of progress of fluid through the additional layercompared to the other slits.

[0059] Where the stiffening element is a metal or bioresorbable stylet,the stiffening sheath can, in one embodiment, be formed from a shapememory alloy or a heat sensitive material. For example, the stiffeningsheath can be formed from a nickel/titanium alloy, or a bimetallicelement formed of a laminate of two different metals, that is shaped totake and maintain the straight or substantially straight configurationof the elongate member at room temperature but bends it into anothershape once it is exposed to body temperature.

[0060] While both the stiffening element and the stiffening sheath arein position within the device, it will retain the first configuration,which as discussed is preferably straight. If the stiffening sheath isremoved or softened, whether it is by dissolution or otherwise, theremaining stiffening element has insufficient strength to retain theelongate member in its first configuration. It is preferred that theelongate member, on removal or softening of the stiffening sheath, willadopt an intermediate configuration in which the elongate member has atleast some curvature.

[0061] The purpose of allowing the elongate member to adopt thisintermediate configuration is to enable the elongate member to beinserted into the cochlea in a way which minimises trauma to the wallsof the cochlea. The preferred shape of this intermediate configurationis for the elongate member to assume a shape that is more curved thanthe straight configuration present upon insertion. By providing thepreviously straight array with a more curved shape, the elongate memberis guided to adopt a mid-scala trajectory as it is inserted into thecochlea. This ensures that as the elongate member is carefully inserteddeeper into the spiral shaped cochlea, the intermediate curvedconfiguration assists in assuring that the elongate member can beinserted deep into the cochlea without causing excessive trauma to thewalls of the cochlea.

[0062] On subsequent removal of the stiffening element, the elongatemember is free to adopt the fully curved second configuration desired ofan implant for final position in the cochlea.

[0063] The present invention provides a surgeon with a means to at leastpartially control the rate of curvature formation in a cochlearelectrode assembly during insertion into the cochlea. Such increasedcontrol is envisaged to reduce the potential for trauma to the cochleacaused by electrode assembly insertion. The present invention alsoprovides a means of assisting the insertion process of the electrodeassembly into the cochlea by allowing the electrode assembly to alterits configuration during the insertion process to allow for deeper andmore desirable cochlea penetration.

[0064] In a further embodiment, at least a portion of an outer surfaceof the elongate member can have a coating of a lubricious material. Inone embodiment, a substantial portion or the entire outer surface of theelongate member can have a coating of the lubricious material.

[0065] In this embodiment, the lubricious material can be selected fromthe group comprising polyacrylic acid (PAA), polyvinyl alcohol (PVA),polylactic acid (PLA) and polyglycolic acid (PGA). It is envisaged thatother similar materials could also be used.

[0066] In a further aspect, the present invention comprises a method ofimplanting a tissue-stimulating device or cochlear electrode assemblydevice as defined herein in a body of an implantee.

[0067] In this aspect, the method can comprise a step of accessing theimplantation site and then a step of inserting the device. Prior toinsertion, the device is preferably substantially straight or straight.On insertion, the device can adopt an intermediate configuration (asdefined herein). Either prior to full insertion or following fullinsertion, the device preferably adopts its second configuration.

[0068] Once implanted, the electrodes can receive stimulation signalsfrom a stimulator means. The stimulator means is preferably electricallyconnected to the elongate member by way of an electrical lead. The leadcan include the one or more wires extending from each electrode of thearray mounted on the elongate member.

[0069] In one embodiment, the lead can extend from the elongate memberto the stimulator means or at least the housing thereof. In oneembodiment, the lead is continuous with no electrical connectors, atleast external the housing of the stimulator means, required to connectthe wires extending from the electrodes to the stimulator means. Oneadvantage of this arrangement is that there is no requirement for thesurgeon implanting the device to make the necessary electricalconnection between the wires extending from the electrodes and thestimulator means.

[0070] The stimulator means is preferably positioned within a housingthat is implantable within the implantee. The housing for the stimulatormeans is preferably implantable within the bony well in the bone behindthe ear posterior to the mastoid.

[0071] When implantable, the housing preferably contains, in addition tothe stimulator means, a receiver means. The receiver means is preferablyadapted to receive signals from a controller means. The controller meansis, in use, preferably mounted external to the body of the implanteesuch that the signals are transmitted transcutaneously through theimplantee.

[0072] Signals can preferably travel from the controller means to thereceiver means and vice versa. The receiver means can include a receivercoil adapted to receive radio frequency (RF) signals from acorresponding transmitter coil worn externally of the body. The radiofrequency signals can comprise frequency modulated (FM) signals. Whiledescribed as a receiver coil, the receiver coil can preferably transmitsignals to the transmitter coil which receives the signals.

[0073] The transmitter coil is preferably held in position adjacent theimplanted location of the receiver coil by way of respective attractivemagnets mounted centrally in, or at some other position relative to, thecoils.

[0074] The external controller can comprise a speech processor adaptedto receive signals output by a microphone. During use, the microphone ispreferably worn on the pinna of the implantee, however, other suitablelocations can be envisaged, such as a lapel of the implantee's clothing.The speech processor encodes the sound detected by the microphone into asequence of electrical stimuli following given algorithms, such asalgorithms already developed for cochlear implant systems. The encodedsequence is transferred to the implanted stimulator/receiver means usingthe transmitter and receiver coils. The implanted stimulator/receivermeans demodulates the FM signals and allocates the electrical pulses tothe appropriate attached electrode by an algorithm which is consistentwith the chosen speech coding strategy.

[0075] The external controller further comprises a power supply. Thepower supply can comprise one or more rechargeable batteries. Thetransmitter and receiver coils are used to provide power viatranscutaneous induction to the implanted stimulator/receiver means andthe electrode array.

[0076] While the implant system can rely on external componentry, inanother embodiment, the controller means, including the microphone,speech processor and power supply can also be implantable. In thisembodiment, the controller means can be contained within a hermeticallysealed housing or the housing used for the stimulator means.

BRIEF DESCRIPTION OF THE DRAWINGS

[0077] By way of example only, preferred embodiments of the inventionare now described with reference to the accompanying drawings, in which:

[0078]FIG. 1 is a simplified cross-sectional view of one embodiment ofan electrode assembly according to the present invention depicted in itsfirst configuration;

[0079]FIG. 2 is a simplified side elevational view of the electrodeassembly of FIG. 1 depicted in an intermediate configuration;

[0080]FIG. 3 is a simplified part-sectional, part side elevational viewof the electrode assembly depicted in its second configuration followinginsertion in the cochlea;

[0081]FIG. 4 is a simplified cross-sectional view of another embodimentof an electrode assembly according to the present invention; and

[0082]FIGS. 5a-5 d depict alternative tip structures for the electrodeassembly depicted in FIG. 4.

PREFERRED MODE OF CARRYING OUT THE INVENTION

[0083] One embodiment of a cochlear implant electrode assembly accordingto the present invention is depicted generally as 10 in the drawings.

[0084] The depicted electrode assembly 10 has an electrical leadextending back to a stimulator/receiver housing. In considering thisinvention, it is to be understood that each electrode may have one ormore wires (not depicted) electrically connected thereto and extendingfrom each respective electrode back through the lead to thestimulator/receiver.

[0085] The assembly 10 comprises an elongate electrode carrier member 11having a plurality of electrodes 12 mounted thereon. For the purposes ofclarity, the electrodes 12 depicted in FIG. 1 are not necessarily shownto scale.

[0086] The depicted elongate member 11 is preformed from a resilientlyflexible silicone with memory and is preformed to a curved configurationsuitable for insertion in the scala tympani of the cochlea. The elongatemember 11 has a first end 13 that is firstly inserted into the cochleaupon insertion of the assembly 10.

[0087] As depicted in FIG. 4, the elongate member 11 can have a tipmember 29 integrally formed with its first end 13. The tip 29 is formedfrom the same silicone used to fabricate the elongate member 11 and, inthe depicted embodiment, the material of tip member 29 has a resilientflexibility equal to that of the material used for the carrier member11.

[0088] Possible alternative constructions for the tip member 29 areprovided in FIGS. 5a-5 d. As depicted in FIG. 5a, the tip member 70 canbe solid and formed of an inner core 71 of relatively stiff material 71and an outer layer 72 of relatively flexible material. The core 71 cantaper in diameter over region 73 towards the distal end 21. The taper 73causes the overall stiffness of the tip 70 to increase over the lengthof the taper 73 away from the distal end 21. The outer layer 72 can beformed of the same material as the remainder of the body of the elongatecarrier member 11 or can be a different material.

[0089] As depicted in FIG. 5b, the tip member 40 can comprise a solidmass integrally formed to the first end 13 of the elongate carrier 11.

[0090] Still further and as depicted in FIG. 5c, the tip member 50 cancomprise a solid mass 51 that is formed separately from the carriermember 11 and subsequently adhered thereto.

[0091] As depicted in FIG. 5d, the tip member 60 can comprise anelastomeric silicone material having a plurality of substantiallyspherical platinum particles 61 dispersed therethrough. The particles 61have a diameter between about 50 μm and 100 μm. It will be appreciatedthat the particles 61 depicted in FIG. 6d are not drawn to scale.

[0092] In FIG. 5d, the particles 61 are depicted as substantially evenlydispersed through the tip member 60. In another embodiment, theparticles could be non-evenly dispersed through the tip member. Forexample, the particles could increase in density away from the distalend 21 towards the proximal end of the tip member 60. By varying thedensity of the platinum particles 61, it is possible to vary therelative stiffness of the tip member 60.

[0093] In addition to, or instead of, being used to potentially modifythe physical characteristics of the tip member, the provision of themetallic particles 61 also result in the tip member 60 being detectableby fluoroscopy and X-ray techniques. This provides another means for thesurgeon to either monitor the placement and position of the tip member60 during or after insertion of the electrode array 10 in an implantee'scochlea.

[0094] Disposed within a lumen 14 is a substantially straight platinumstylet 15. The stylet 15 alone has a stiffness that is insufficient toretain the silicone elongate member 11 in a straight configuration.

[0095] While a platinum stylet is depicted, a bioresorbable styletformed from a bioresorbable polyacrylic acid (PAA) that is adapted todissolve or soften on exposure to cochlear fluids could be utilised withappropriate modification to the elongate carrier member 11. Equally,whilst a substantially cylindrical lumen is depicted, the lumen 14 couldindeed be any shape necessary to perform the function. Again, the PAAstylet in this invention has a stiffness insufficient to retain thesilicone elongate member 11 in a straight configuration as depicted inFIG. 1. It will be appreciated that a bioresorbable stylet could beformed from other suitable bioresorbable materials. A stylet made from ashape memory alloy or heat sensitive material could also be utilised asa stylet 15.

[0096] Overlaying the depicted elongate member 11 is a stiffening sheath16 of bioresorbable material. The bioresorbable material of the depictedstiffening sheath 16 is PAA that is adapted to dissolve on exposure tocochlear fluids. Other suitable bioresorbable materials can be envisagedand such materials need not necessarily dissolve on exposure to fluids,the current invention could also function correctly if the sheath 16 ismade of a material that softens upon exposure to fluids but does not getabsorbed.

[0097] While the elongate member 11 is manufactured with a preformedcurved configuration, the assembly 10 is typically delivered to asurgeon with the stylet 15 and sheath 16 in place. The combination ofthe stylet 15 and sheath 16 is sufficient to hold the elongate member 11in the straight configuration depicted in FIG. 1.

[0098] On insertion into the scala tympani of the cochlea 30, thecochlear fluids commence to dissolve or soften the sheath 16. As the PAAsoftens and dissolves, the elongate member 11 commences to re-curl (seeFIG. 2) as the stiffness of the stylet 15 is insufficient to hold theelongate member 11 straight. The provision of the stylet 15 within theelongate member 11 does, however, prevent the elongate member 11 fromadopting its pre-formed spirally curved configuration.

[0099] As the elongate member 11 curls, the surgeon can continue tofurther insert the assembly 10 into the scala tympani 31 with a lessenedrisk of the member 11 puncturing fine tissues of the cochlea 30. It ispossible that during the further insertion process the surgeon maysimultaneously withdraw the platinum stylet 15 through the opening 17 ofthe lumen 14 at end 18. On withdrawal of the stylet 15, the elongatemember 11 is free to adopt the spiral configuration depicted in FIG. 3with the electrodes facing the modiola within the cochlea 30 so thatthey are positioned as close as possible to the spiral ganglia thereof.

[0100] It is also envisaged that in one arrangement the surgeon maywithdraw the stylet 15 first and rely upon the sheath 16 to maintain thearray in the intermediate position.

[0101] The combination of the stiffening element 15 and stiffeningsheath 16 provides the surgeon with greater control of the implantationprocedure for the cochlear implant electrode assembly 10. The provisionof greater control minimises the potential for trauma to the sensitivetissues inside the cochlea and also enhances the likelihood ofsuccessful placement of the assembly 10 at the first attempt.

[0102] While the preferred embodiment of the invention has beendescribed in conjunction with a cochlear implant, it is to be understoodthat the present invention has wider application to other implantableelectrodes, such as electrodes used with pacemakers.

[0103] It will be appreciated by persons skilled in the art thatnumerous variations and/or modifications may be made to the invention asshown in the specific embodiments without departing from the spirit orscope of the invention as broadly described. The present embodimentsare, therefore, to be considered in all respects as illustrative and notrestrictive.

1. An implantable tissue-stimulating device comprising: an elongatemember having a plurality of electrodes mounted thereon and having afirst configuration that allows said member to be inserted into animplantee's body, a second configuration wherein said elongate member isadapted to apply a preselected tissue stimulation with the electrodes,and at least one intermediate configuration between said first andsecond configurations, said elongate member being made of a resilientlyflexible first material; a stiffening element made of a materialrelatively stiffer than said first material; and a stiffening sheath atleast partially enveloping said elongate member and made of a materialrelatively stiffer than said first material; wherein said stiffeningelement and said stiffening sheath in combination bias said elongatemember into said first configuration and further wherein if either thestiffening element or the stiffening sheath is removed or deactivated,the elongate member adopts said at least one intermediate configuration.2. A cochlear implant electrode assembly device comprising: an elongateelectrode carrier member having a plurality of electrodes mountedthereon and having a first configuration that allows said member to beinserted into an implantee's cochlea, a second configuration whereinsaid elongate member is curved to match an inside surface of saidcochlea, and at least one intermediate configuration between said firstand second configurations, said elongate member being made of aresiliently flexible first material; a stiffening element made of amaterial relatively stiffer than said first material; and a stiffeningsheath at least partially enveloping said elongate member and made of amaterial relatively stiffer than said first material; wherein saidstiffening element and said stiffening sheath in combination bias saidelongate member into said first configuration and further wherein ifeither the stiffening element or the stiffening sheath is removed ordeactivated, the elongate member adopts said at least one intermediateconfiguration.
 3. A device of claim 1 or claim 2 wherein the secondconfiguration of the elongate member is curved.
 4. A device of claim 3wherein the elongate member adopts a spiral configuration when in thesecond configuration.
 5. A device of claim 1 or claim 2 wherein theelongate member is preformed from a plastics material with memory and ispreformed to the second or intermediate configuration.
 6. A device ofclaim 1 or claim 2 wherein the elongate member has a first end that isfirstly inserted into the implantee.
 7. A device of claim 1 or claim 2wherein the first configuration is at least substantially straight.
 8. Adevice of claim 1 or claim 2 wherein the elongate member is formed froma biocompatible material.
 9. A device of claim 8 wherein thebiocompatible material is selected from the group comprising a siliconeand a polyurethane.
 10. A device of claim 1 or claim 2 wherein thestiffening element is formed of a bioresorbable material which softensor dissolves on exposure to a fluid.
 11. A device of claim 10 whereinthe stiffening element softens or dissolves on exposure to a salinesolution or a body fluid of the implantee.
 12. A device of claim 11wherein the bioresorbable material of the stiffening element is selectedfrom the group comprising polyacrylic acid (PAA), polyvinyl alcohol(PVA), polylactic acid (PLA) and polyglycolic acid (PGA).
 13. A deviceof claim 1 or claim 2 wherein the stiffening element is formed from anon-bioresorbable material.
 14. A device of claim 13 wherein thestiffening element is a stylet extending through a lumen in the elongatemember.
 15. A device of claim 14 wherein the stylet is formed from abiocompatible material selected from the group comprising a metal, ametallic alloy and a stiff plastic.
 16. A device of claim 15 wherein thestylet is formed from platinum.
 17. A device of claim 1 or claim 2wherein the stiffening element is formed from a shape memory material.18. A device of claim 1 or claim 2 wherein the stiffening sheath isformed of a bioresorbable material which dissolves or softens onexposure to a fluid.
 19. A device of claim 18 wherein the bioresorbablematerial of the stiffening sheath is selected from the group comprisingpolyacrylic acid (PAA), polyvinyl alcohol (PVA), polylactic acid (PLA)and polyglycolic acid (PGA).
 20. A device of claim 19 wherein anadditional layer surrounds the stiffening sheath.
 21. A device of claim20 wherein the additional layer has a first rate of fluid ingresstherethrough and at least one fluid ingress means formed therein, therate of fluid ingress through the fluid ingress means being greater thanthe first rate of fluid ingress through the additional layer.
 22. Adevice of claim 21 wherein the fluid ingress means comprises one or moreopenings in the additional layer.
 23. A device of claim 1 or claim 2wherein at least a portion of an outer surface of the elongate memberhas a coating of a lubricious material.
 24. A device of claim 23 whereina substantial portion or the entire outer surface of the elongate memberhas a coating of the lubricious material.
 25. A device of claim 23wherein the lubricious material is selected from the group comprisingpolyacrylic acid (PAA), polyvinyl alcohol (PVA), polylactic acid (PLA)and polyglycolic acid (PGA).
 26. A device of claim 6 wherein aresiliently flexible tip member extends forwardly from the first end ofthe elongate member.
 27. A device of claim 26 wherein the tip member hasa plurality of metallic particles dispersed therethrough.